Prometryn

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

01 Apr 997 to 31 Jul 1997

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Version / remarks:

1982

GLP compliance:

yes

Radiolabelling:

yes

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 300 - <= 400

Relative light intensity:

58.02

Reference substance:

yes

Dark controls:

yes

% Degr.:

7

Sampling time:

36 d

Test condition:

irradiated soil

Remarks on result:

other: degraded to M2

% Degr.:

10

Sampling time:

36 d

Test condition:

irradiated soil

Remarks on result:

other: degraded to M4

% Degr.:

8

Sampling time:

36 d

Test condition:

irradiated soil

Remarks on result:

other: degraded to M12 and M12a

DT50:

136 d

Test condition:

irradiated water

Remarks on result:

other: under natural summer sunlight exposure at latitudes between 30° N (Florida) and 50° N, assuming 12 hours of daylight

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Recovery

- On average 94.6 ± 2.1 % and 96.5 ± 1.6 of the applied radioactivity was recovered in the irradiated samples for the two experiments (dark controls: 93.7% and 96.6%). The corresponding overall production of volatile radioactive products was < 1 %. Dark controls did not produce volatile products.

- Sterility: In none of the experiments any growth of bacteria was observed after 36 days.

- pH: Remained at about 7

 

Kinetics

- Aqueous photolysis: The parent decay could be described by an overall half-life of 59 days (correlation coefficient = 0.98). Since the xenon arc emission spectrum mimics that of natural sunlight the suntest light intensity could be related to that of natural summer sunlight at latitudes between 30° N (Florida, USA) and that of natural summer sunlight at latitude 50° N. Thus, 59 days suntest irradiation equal 136 days of summer sunlight irradiation.

- Dark control experiments: Dark control experiments showed no degradation of the test compound.

 

Photoproducts

- Besides minor, negligible degradates three significant degradation fractions (M2, M4 and M12) formed, reaching at highest 7, 10 and 8% at the end of the study. M12 is likely to be a mixture, which include M12 and the reduced parent M12a. The identity of the parent peak was confirmed by LC - MS.

Table 1. Recovery of the Radioactivity applied for the Aqueous Photolysis of 14C- labelled test substance

Sampling time (d)	Irradiated						Dark control (DC)
	Photolysis A	Volatiles A	Recovery A	Photolysis B	Volatiles B	Recovery B	A	B
0	96.55	0.00	96.55	97.62	0.00	97.62	92.18	97.14
2	95.32	0.00	95.32	97.65	0.00	97.65
7	96.14	0.01	96.15	95.52	0.01	95.52
10	95.95	0.01	95.96	94.50	0.01	94.51
14	93.78	0.01	93.79	98.07	0.01	98.08	95.19	96.01
21	94.43	0.02	94.45	98.09	0.02	98.11
36	89.72	0.09	89.81	93.90	0.09	93.98
Recovery	94.58 ± 2.14			96.50 + 1.64			93.369	96.58

 

Validity criteria fulfilled:

not specified

Conclusions:

The test substance was slowly broken down by light with a half-life of 136 days (midsummer sunlight at latitude 30 - 50°N). Besides minor, insignificant degradates 3 – 4 significant photo-degradates were observed, none of them exceeding 10 % of the applied dose.

Executive summary:

The photolytic degradation of the test substance was evaluated in 0.007M phosphate buffer (pH 7) at a concentration of 5 ppm at 25°C under xenon arc light. The study was conducted according to guideline EPA 161 -2 and it was compliant with GLP. On average, 94.6 ± 2.1 % and 96.5 ± 1.6% of the applied radioactivity was recovered in the irradiated samples (two experiments). The corresponding values for the dark controls were 93.7 % and 96.6 %. Less than 1% of the test substance applied could be detected as volatile radioactivity. Dark controls did not produce any volatile products. Besides several minor, negligible photodegradation products, three significant fractions were found: 7% M2 at highest at the end of the study), 10% M4 at highest at the end of the study and a mixture of two compounds: M12 and the reduced parent M12a (8 % for the whole mixture at highest at the end of the study). The photolytical half-life of the test substancewas determined to be 59 days under “Suntest" irradiation equivalent to 136 days under natural summer sunlight exposure at latitudes between 30° N (Florida) and 50° N, assuming 12 hours of daylight.

Reference 2

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

30 Aug 1987 to 18 Dec 1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Study type:

direct photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

- This study was conducted according to the test facility's protocol named "Solution Photolysis of the test substance in Natural Sunlight", to partially fulfil the registration requirements set forth by the U.S. Environmental Protection Agency Guidelines (Subdivision N).
- Deviations in study protocol: 1) The protocol states that the test solution will be prepared at 25 ppm of [14C]-labelled test substance. The actual concentration of [14C]-labelled test substance in the test solution was 1.74 ppm. One percent dioxane was added as a cosolvent. These changes were discussed with the Sponsor and were made due to the insolubility of the test substance at 25 ppm in pH 7.0 buffer. 2) The protocol states that samples will be radioassayed on a Packard Model 1500 LSC. Samples were radioassayed on a Packard Model 4430 LSC which also automatically converts cpm to dpm using computer-constructed quench curves derived from a series of ten sealed quenched standards. 3) The protocol states that three aliquots (1 mL) will be removed from each sample for radioassay when three aliquots of 0.5 mL were, in fact, removed from each sample. This change should have no impact on the findings of this study

GLP compliance:

yes

Radiolabelling:

yes

Light source:

sunlight

Light spectrum: wavelength in nm:

>= 220 - <= 400

Relative light intensity:

> <

Reference substance:

yes

Dark controls:

yes

% Degr.:

2.19

Sampling time:

30 d

Test condition:

irradiated water

Remarks on result:

other: degraded to M2

% Degr.:

1.89

Sampling time:

30 d

Test condition:

irradiated water

Remarks on result:

other: degraded to unknown photoproduct

% Degr.:

0

Sampling time:

30 d

Test condition:

dark control

DT50:

> 30 d

Test condition:

irradiated soil

Transformation products:

yes

No.:

#1

Radiochemical purity

- The radiochemical purity of [14C]-labelled test substance as determined by HPLC analysis was 98.5%.

- Temperature: 22.4 + 0.6° C

- Cumulative light energy: 6 - 26 W·min/cm2 per day

- An overview of the reuslts in provided in Table 1 - Table 3 below.

Material Balance

- Throughout the study no radiocarbon was detected in the ethylene glycol, H2SO4 or NaOH traps.

- Total recovery of radiocarbon for all samples ranged between 75 and 99% of the amount added to individual tubes. The mean + S.D. was 87 + 6.7%. There were no volatile products detected from any sample, therefore, it was not necessary to consider trap recoveries in the material balance. There was little change in pH of the solutions over the 30 day period. The pH of some solutions decreased to 6.8.

 

[14C]- labelled test substance and Its Photoproducts

- HPLC analysis revealed that in all cases > 95% of the total recovered radiocarbon present in irradiated and dark control samples was identified as [14C]-labelled test substance.A small amount of M2 (< 3%) was identified in irradiated samples at Day 15 and later time points. An unknown degradate was also detected in small amounts (< 4%) in those same samples.Thin layer chromatography confirmed the identities of [14C]-labelled test substance and M2. The unknown degradate co-chromatographed with M10 on TLC, but its retention time by HPLC was not the same as for the M10 reference standard.

 

Photodegreadation

- Because less than 10% degradation was observed over the 30-day exposure period, the test substance is considered to be photolytically stable in solution In samples irradiated 30 days the total recovered radiocarbon when subjected to HPLC indicated 95.91% was [14C]-labelled test substance, 2.19% was [14C]-labelled M2 and 1.89% was an unknown photoproduct. The total recovered radiocarbon was 100% [14C]-labelled test substance in those samples maintained 30 days in the dark. Contamination may have been the basis for the slight degradation observed in Day 15 Dark Control Replicate 1. Its degradate did not co-chromatograph with anything seen in any other radiochromatogram. All other samples maintained in the dark showed no degradation indicating that the reaction observed inirradiated tubes was photochemically mediated. The half-life was greater than 30 days.

Table 1. Accountability of Radiocarbon Throughout Aqueous Photolysis Study

Sample Description	Total DPM Applied	Total DPM Present At Sample Time	Total recovery %
Day 0
Irradiated 1	1,125,740	1,056,399	94
Irradiated 2	1,125,740	1,110,571	99
Dark control 1	1,125,740	1,068,622	95
Dark control 2	1,125,740	1,058,969	94
Day 5
Irradiated 1	1,125,740	1,047,230	93
Irradiated 2	1,125,740	990,986	88
Dark control 1	1,125,740	1,012,387	90
Dark control 2	1,125,740	1 ,022,180	91
Day 10
Irradiated 1	1,125,740	851,887	76
Irradiated 2	1,125,740	849,132	75
Dark control 1	1,125,740	872,669	78
Dark control 2	1,125,740	839,177	75
Day 15
Irradiated 1	1,125,740	910,655^1	81
Irradiated 2	1,125,740	885,273^1	79
Dark control 1	1,125,740	922,685^1	82
Dark control 2	1,125,740	946,067^1	84
Day 20
Irradiated 1	1,125,740	997,444	89
Irradiated 2	1,125,740	996,059	88
Dark control 1	1,125,740	1,011,280	90
Dark control 2	1,125,740	996,888	89
Day 30
Irradiated 1	1,125,740	1,013,432	90
Irradiated 2	1,125,740	1,019,715	91
Dark control 1	1,125,740	1,002,436	89
Dark control 2	1,125,740	1,028,720	91
Mean + S.D.			87 ± 6.7

1. Tabulation does not include a cocktail wash of tube

 

Table 2. Quantitative Characterization of [14C]-labelled test substance and Its Products As Determined by HPLC.

Sample description	The test substance	M9	Unknown
Day 0
Irradiated 1	97.68	N.D.^1	2.33
Irradiated 2	100.00	N.D.	N.D.
Mean	98.84	N.D.	1.17
Dark control 1	100.00	N.D.	N.D.
Dark control 2	100.00	N.D.	N.D.
Mean	100.00	N.D.	N.D.
Day 5
Irradiated 1	100.00	N.D.	N.D.
Irradiated 2	100.00	N.D.	N.D.
Mean	100.00	N.D.	N.D.
Dark control 1	100.00	N.D.	N.D.
Dark control 2	100.00	N.D.	N.D.
Mean	100.00	N.D.	N.D.
Day 10
Irradiated 1	98.53	N.D.	1.47
Irradiated 2	99.16	N.D.	0.84
Mean	98.85	N.D.	1.16
Dark control 1	100.00	N.D.	N.D.
Dark control 2	100.00	N.D.	N.D.
Mean	100.00	N.D.	N.D.
Day 15
Irradiated 1	96.54	0.69	2.78
Irradiated 2	97.67	0.74	1.59
Mean	97.11	0.72	2.19
Dark control 1	94.65	N.D.	5.35
Dark control 2	100.00	N.D.	N.D.
Mean	97.33	N.D.	2.68
Day 20
Irradiated 1	94.31	2.12	3.58
Irradiated 2	96.41	0.64	2.94
Mean	95.36	1.38	3.26
Dark control 1	100.00	N.D.	N.D.
Dark control 2	100.00	N.D.	N.D.
Mean	100.00	N.D.	N.D.
Day 30
Irradiated 1^2	---	---	---
Irradiated 2	95.91	2.19	1.89
Mean	---	---	---
Dark control 1	100.00	N.D.	N.D.
Dark control 2	100.00	N.D.	N.D.
Mean	100.00	N.D.	N.D.

1.None detected. Detection limit: 30 dpm or 0.465 ng of the test usbtance

2.Due to a printing error, integration of radiochromatographic data was unavailable. However, visual inspection of the radiochromatograph indicates close similarity to the duplicate sample.

 

Table 3. Confirmation of the Identities of [14C]-labelled test substance and Its Metabolites by Thin Layer Chromatography

Percent of Total Radiocarbon Which Migrates With Authentic Reference Standards of:^1
Sample Description^2	The test substance	M2	M10	M4 and M9
A	93.51	2.64	2.85	0.98
B	93.78	2.71	2.68	0.80

1.Sample used for confirmation was Day 30 Irradiated sample Replicate 2. "A" and "B" refer to TLC duplicates

2. Rf values obtained for authentic reference standards are as follows: The test substance: 0.77; M9: 0.47; M10: 0.73; M11: 0.75; M12: 0.66

Validity criteria fulfilled:

not specified

Conclusions:

The half-life for the photochemical reaction in natural sunlight is greater than 30 days. The only photoproduct identified was [14C]-labelled M2 which comprised 2.19% of the total recovered radiocarbon in irradiated samples. An unknown photoproduct was attributable to the remaining 1.89% of the total recovered radiocarbon.

Executive summary:

The photodegradation of [14C]-labelled test substance was investigated in quartz tubes as an aqueous solution at pH 7.0 (directly expose to natural sunlight) for 30 days. The study was conducted in compliance with GLP but no guidelines was followed. The quartz tubes were exposed to direct sunlight on the roof of the test facility (latitude - 38.05N; longitude - 84.30W), where they remained throughout the study period.The tubes were oriented at a 30° angle with respect to the horizontal such that the length of each tube was facing south perpendicular to the sun's path. The study was carried out in 22.4 + 0.6° C and with 6 - 26 W·min/cm2 per day cumulative light energy.The final concentration of [14C]-labelled test substance in the test solution was 1.1 x 105 dpm/mL or 1.74 ppm (µg/mL). The radiochemical purity of [14C]-labelled test substance as determined by HPLC analysis was 98.5%. After 30 days 95.91% of the total recovered radiocarbon remained as [14C]-labelled test substance in the irradiated samples; 100% remained as [14C]-labelled test substance in the dark controls. The only photoproduct identified was [14C]-labelled M2 which comprised 2.19% of the total recovered radiocarbon in irradiated samples. An unknown photoproduct was attributable to the remaining 1.89% of the total recovered radiocarbon. The half-life for the photochemical reaction in natural sunlight is greater than 30 days.

Reference 3

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

28 Jan 2005 to 21 Dec 2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

indirect photolysis

Qualifier:

according to guideline

Guideline:

other: OECD Guidelines for the Testing of Chemicals, Phototransformation of Chemicals in Water- Direct and Indirect Photolysis

Version / remarks:

Draft new guideline, August 2000

GLP compliance:

yes

Radiolabelling:

yes

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 300 - <= 400

Relative light intensity:

38.51

Reference substance:

yes

Dark controls:

yes

% Degr.:

18.95

Sampling time:

8 d

Test condition:

irradiated soil

Remarks on result:

other: degradated to M4

% Degr.:

7.41

Sampling time:

8 d

Test condition:

Irradiated soil

Remarks on result:

other: degradated to M5

% Degr.:

4.88

Sampling time:

8 d

Test condition:

irradiated soil

Remarks on result:

other: degradated to M13 and M14

% Degr.:

8.66

Sampling time:

8 d

Test condition:

irradiated soil

Remarks on result:

other: degradated to M2

% Degr.:

1.16

Sampling time:

8 d

Test condition:

irradiated soil

Remarks on result:

other: unknown metabolite

% Degr.:

6.62

Sampling time:

8 d

Test condition:

irradiated soil

Remarks on result:

other: unknow metabolities with mass 195 and mass 257

DT50:

7.1 d

Test condition:

irradiated natural water

Remarks on result:

other: continuous irradiation under the Suntest

DT50:

7.7 d

Test condition:

Irradiated natural water

Remarks on result:

other: continuous irradiation under the Suntest

DT50:

11.8 d

Test condition:

irradiated natural water

Remarks on result:

other: converted into days of natural summer sunlight at 30°N

DT50:

35 d

Test condition:

irradiated natural water

Remarks on result:

other: converted into days of natural spring sunlight at 35°N

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Average recoveries of 94 - 99% of the applied radioactivity were found in the duplicate natural water samples at each time point. Insignificant amounts of radioactivity (0% of applied) were found to be present in the NaOH traps used to trap any 14CO2 produced and since good recoveries were obtained, the carbon sieves used to capture volatile organic compounds were not analysed.

The amount of the test substance in the irradiated natural water samples decreased from 94.72% at the start of the experiment (T = 0 DAT) to 48.83% after 8 days irradiation under the Suntest. The amount of the test substance remaining at each time point was fitted to simple first order kinetics. DT50 and DT90 values of 7.1 and 23.5 days continuous irradiation under the Suntest were obtained respectively. On conversion into days of natural spring sunlight at 35°N, DT50 and DT90 values of 35.0 and 116.4 days respectively were obtained.

Only one major photodegradate was observed at levels that exceeded 10% of the applied radioactivity at any point in the test. This photolysis product was identified as M4 by comparison with an authenticated reference item using LC-MS-MS. Seven other chromatographic peaks were observed at the various time points, none of which exceeded 10% of the applied radioactivity at any time in the test.

Very little degradation was observed in the 8 DAT dark control samples, since 93.39% of the applied radioactivity was present as the test substance. Two minor components were observed which, in total, comprised less than 3% of the applied radioactivity. Sterile conditions were maintained throughout the photolysis period.

Conclusions:

Based on the findings, the amount of the test substance remaining at each time point was fitted to simple first order kinetics. DT50 and DT90 values of 7.1 and 23.5 days continuous irradiation under the Suntest were obtained respectively. On conversion into days of natural spring sunlight at 35°N, DT50 and DT90 values of 35.0 and 116.4 days respectively were obtained. Only one major photodegradate was observed at levels that exceeded 10% of the applied radioactivity at any point in the test. This photolysis product was identified as M4 by comparison with an authenticated reference item using LC-MS-MS.

Executive summary:

The photolysis of the test substance in sterile natural water was investigated in according to OECD draft guideline and in compliance with GLP. 14C-labelled test substance was applied to Middle Row Pond natural water to give a nominal concentration of 5µg/mL. Treated samples were continuously irradiated using light from a xenon arc lamp, which was filtered to give a spectral distribution close to that of natural sunlight. Samples were maintained at 25 ± 2°C and irradiated for defined periods of up to 8 days under the Suntest, which was calculated to be the equivalent of approximately 40 days spring sunlight at a latitude of 35°N.

Duplicate samples were analysed after approximately 0, 1, 2, 4, 5, 7 and 8 days irradiation under the Suntest. Duplicate non-irradiated dark control samples were also prepared and maintained at 25 ± 2°C for approximately 8 days. The test substance underwent photolysis in sterile natural water. Average recoveries of 94 - 99% of the applied radioactivity were found in the duplicate natural water samples at each time point. The amount of the test substance in the irradiated natural water samples decreased from 94.7% at the start of the experiment (T = 0 DAT) to 48.8% after 8 days irradiation under the Suntest. The amount of the test substance remaining at each time point was fitted to simple first order kinetics and DT50 and DT90 values of 7.1 and 23.5 days continuous irradiation under the Suntest were obtained respectively. On conversion into days of natural spring sunlight at 35°N, DT50 and DT90 values of 35.0 and 116.4 days respectively were obtained.

Only one major photodegradate was observed at levels that exceeded 10% of the applied radioactivity throughout the test. This photolysis product was identified as M4 by comparison with an authenticated reference item using LC-MS-MS. Seven other chromatographic peaks were observed at the various time points, none of which exceeded 10% of the applied radioactivity at any time in the test. Very little degradation was observed in the 8 DAT dark control samples, since 93.4% of the applied radioactivity was present as the test substance. Two minor components were observed which, in total, comprised less than 3% of the applied radioactivity. In addition, a further two samples were irradiated under the Suntest for 26 days, which was calculated to be the equivalent of 40 days summer sunlight at 30°N. Duplicate non-irradiated dark control samples were also prepared and maintained at 25 ± 2°C for approximately 26 days. Average recoveries of 91 - 99% of the applied radioactivity were found in the duplicate natural water samples at each time point.

The amount of the test substance in the irradiated natural water samples decreased from 94.7% at the start of the experiment (T = 0 DAT) to 17.8% after 26 days irradiation under the Suntest. Using simple first order kinetics, DT50 and DT90 values of 7.7 and 25.7 days continuous irradiation under the Suntest were obtained respectively. These values were converted into days of summer sunlight at 30°N, 40°N and 50°N. Under natural summer sunlight conditions, DT50 and DT90 values of 11.8 and 39.1 days respectively were obtained at 30°N, 11.6 and 38.4 days respectively at 40°N and 12.2 and 38.4 days respectively at 50°N.

In addition to the parent peak, four other major chromatographic peaks were observed which reached levels of radioactivity that exceeded 10% of applied. Three of these chromatographic peaks were identified as M2, M4 and M5 by comparison with authenticated reference items using LC-MS-MS. The fourth major peak was found to be amixture of M13 and M14 bycomparison with authenticated reference items using LC-MS-MS. Further HPLC separation of these two compounds enabled their relative amounts to be estimated. The ratio of M14:M13 was found to be approximately 3:2 and hence these two compounds were estimated to contribute 8.9% and 5.9% of the applied radioactivity in the 26 DAT samples respectively. Five further chromatographic peaks were observed which contained levels of radioactivity that did not exceed 10% (maximum of 7.7%) of the applied radioactivity over the course of the test. No degradation was observed in the non-irradiated 26 DAT dark control samples.

Throughout all the irradiation periods, insignificant amounts of radioactivity (0% of applied) were found to be present in the NaOH traps used to trap any 14CO2 produced and since good recoveries were obtained, the carbon sieves used to capture volatile organic compounds were not analysed. Sterile conditions were maintained throughout the photolysis period.

Description of key information

Laboratory studies indicate that the test substance is only slightly sensitive to direct photolysis as measured in buffered solution. However, the test substance is sensitive to indirect photolysis as measured in laboratory studies with natural waters resulting in calculated DT50 values between 11.8 and 35 days in spring/summer sunlight at 30 - 35°N. Photolysis may accelerate degradation of the test substance in natural aquatic systems in spring/summer time.